1. Field of the Invention
The present invention relates to an anti-electrolytic corrosion type rolling bearing for use in, for example, a motor or a truck of a railway rolling stock.
2. Description of the Related Art
With a rolling bearing for use in the motor or axle of a railway rolling stock, when a current collector for current grounding, which permits a current from the motor to flow from a wheel to a rail to be grounded, functions insufficiently or improperly, the motor current flows through the rolling bearing to a wheel, then to the associated rail to be grounded therethrough. This is likely to cause a rolling element of the bearing to spark between the rolling face of the outer ring and that of the inner ring. In other words, a so-called electrolytic corrosion occurs. This phenomenon certainly wear out the bearing faster.
As a solution to this shortcoming, there is a technique proposed and disclosed in, for example, Published Unexamined Japanese Utility Model No. 60-85626, in which an insulating layer is formed on the outer surface and both side walls of the outer ring of a rolling bearing for a traction motor of a railway rolling stock and those of the inner ring by sputtering of melt ceramics and an insulating synthesized resin is contained in the insulating layer.
The ceramic material for the insulating layer, which may be alumina, gray alumina, zirconia or the like, is not easily adapted to the material for the bearing and thus is not easily adhered thereto.
Because the outer ring of the bearing in use is fitted in a bearing box, the insulating layer formed on the outer ring requires that, after sputtering, its outer surface be ground to a predetermined thickness and accuracy suitable for the inner wall of the bearing box. Due to the hardness and brittleness of the material for the insulating layer, the process of grinding the insulating layer to the final thickness requires a considerable number of steps and time. Further, in fitting the bearing with an insulating layer formed thereon into the bearing box, some force or pressure needs to be applied and this pressure is apt to separate the insulating layer from the bearing.